<html xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><head><meta http-equiv=Content-Type content="text/html; charset=utf-8"><meta name=Generator content="Microsoft Word 15 (filtered medium)"><style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
{font-family:Aptos;}
@font-face
{font-family:Tahoma;
panose-1:2 11 6 4 3 5 4 4 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
font-size:12.0pt;
font-family:"Aptos",sans-serif;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
span.gmaildefault
{mso-style-name:gmail_default;}
span.EmailStyle19
{mso-style-type:personal-reply;
font-family:"Calibri",sans-serif;
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
--></style></head><body lang=EN-US link=blue vlink=purple style='word-wrap:break-word'><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> John Clark <johnkclark@gmail.com> <br><b>Sent:</b> Sunday, 25 January, 2026 5:23 AM<br><b>To:</b> ExI chat list <extropy-chat@lists.extropy.org><br><b>Cc:</b> spike@rainier66.com; Ben Zaiboc <benzaiboc@proton.me><br><b>Subject:</b> Re: [ExI] Von Neumann Probes<o:p></o:p></span></p></div><p class=MsoNormal><o:p> </o:p></p><div><div><div><p class=MsoNormal><span style='font-family:"Arial",sans-serif'><o:p> </o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><div><p class=MsoNormal>On Sat, Jan 24, 2026 at 6:11<span style='font-family:"Arial",sans-serif'> </span>PM spike jones via extropy-chat <<a href="mailto:extropy-chat@lists.extropy.org">extropy-chat@lists.extropy.org</a>> wrote:<o:p></o:p></p></div><p class=MsoNormal><o:p> </o:p></p><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in'><p class=MsoNormal><span class=gmaildefault><i><span style='font-size:13.5pt;font-family:"Arial",sans-serif'>> </span></i></span><i><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'>The other thing I'm trying to understand is how a bacterium-sized probe<br>travelling at 1%c would last more than a few decades in interstellar space.<br>Just one single collision with a grain of dust would destroy it.</span></i><o:p></o:p></p></blockquote><div><p class=MsoNormal><o:p> </o:p></p></div><p class=MsoNormal><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'>According to Osmanov, although the logic (machinery) of A Von Neumann probe would theoretically only need a picogram of mass (10^-12 gram<span class=gmaildefault>s</span>), to be practical the probe would require about 10^-3 grams, the size and mass of a grain of coarse sand. The extra mass would be used to make a Graphene shield needed to protect the probe from collisions with dust particles<span class=gmaildefault>.</span></span></b><o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'>John K Clark<o:p></o:p></span></b></span></p><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'><o:p> </o:p></span></b></span></p><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'><o:p> </o:p></span></b></span></p><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'><o:p> </o:p></span></b></span></p><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'>At .01c any collision with a dust particle or any particle consisting of even a few thousand atoms would make the material in the shield irrelevant. Reasoning: do a calculation or even a reasonable estimate on the energy of collision, compare with the chemical bonding energy of whatever material you want or can plausibly imagine.<o:p></o:p></span></b></span></p><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'><o:p> </o:p></span></b></span></p><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'>Here’s a paper on high speed collision, which is behind a paywall, but the introduction gives you an idea of what I am talking about: <o:p></o:p></span></b></span></p><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'><o:p> </o:p></span></b></span></p><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'><a href="https://asmedigitalcollection.asme.org/fluidsengineering/article-abstract/95/2/276/412692/Hydrodynamic-Phenomena-During-High-Speed-Collision?redirectedFrom=fulltext">https://asmedigitalcollection.asme.org/fluidsengineering/article-abstract/95/2/276/412692/Hydrodynamic-Phenomena-During-High-Speed-Collision?redirectedFrom=fulltext</a><o:p></o:p></span></b></span></p><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'><o:p> </o:p></span></b></span></p><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'>More relevant than drag is erosion during interstellar travel, never mind what shield material is used (Arthur C Clarke proposed water ice.) Consider a comment Keith made a few days ago about how leaking steam behaves in a powerplant. Estimate the velocity of steam escaping from a small leak, then consider his description of the escaping steam sawing off broomsticks. The local machine shop had a tool for carving metal blocks using a hypervelocity water jet. How many C is that? Any reasonable estimate will do: a kilometer per second? Two? Ten? Regardless of your reasonable estimate, it is still down in the range of a few micro-C. <o:p></o:p></span></b></span></p><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'><o:p> </o:p></span></b></span></p><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'>In light of that thought experiment, think of how absurd was my own calculation yesterday on the deceleration of the cubic millimeter one milligram probe from drag (sheesh, do I feel silly now.) The drag from interstellar hydrogen is irrelevant if the probe burns up or erodes away long before its centuries-long journey at 10 milli-C. <o:p></o:p></span></b></span></p><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'><o:p> </o:p></span></b></span></p><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'>The energy in a collision increases as the square of the velocity. Even intentionally overestimating the velocity of the water jet cutter gives us at least a three order of magnitude velocity ratio, which means a six order of magnitude ratio in energy of collision, taking us into energy levels far greater than the piddly covalent bond energy in diamond or whatever other material you prefer. Ja I know the water jet is orders of magnitude more particles, however it does its precision erosion is orders of magnitude less time than the interstellar probe will be in flight.<o:p></o:p></span></b></span></p><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'><o:p> </o:p></span></b></span></p><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'>Do offer a mathematically based refutation to my conclusion that any millimeter scale von Neumann probe at anywhere near .01C is completely impossible, regardless of any plausible future materials breakthroughs. I might buy the notion of a micro-C however, and if so, it is much easier to imagine accelerating that milligram mass to that velocity and decelerating upon arrival. It shouldn’t matter much if it takes millions of years to span the distance between the closest stars, ja? What’s the big hurry?<o:p></o:p></span></b></span></p><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'><o:p> </o:p></span></b></span></p><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'>John, Keith, Ben, others, what say ye?<o:p></o:p></span></b></span></p><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'><o:p> </o:p></span></b></span></p><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'>spike <o:p></o:p></span></b></span></p><p class=MsoNormal><span class=gmaildefault><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'><o:p> </o:p></span></b></span></p><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in'><p class=MsoNormal><o:p> </o:p></p></blockquote></div></div></div></body></html>